//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++03, c++11, c++14, c++17

// <span>

// template<size_t Offset, size_t Count = dynamic_extent>
//   constexpr span<element_type, see below> subspan() const;
//
// constexpr span<element_type, dynamic_extent> subspan(
//   size_type offset, size_type count = dynamic_extent) const;
//
// Mandates: Offset <= Extent && (Count == dynamic_extent || Count <= Extent - Offset) is true.

#include <span>
#include <cassert>
#include <algorithm>
#include <string>

#include "test_macros.h"

template <typename Span, std::size_t Offset, size_t Count>
constexpr bool testConstexprSpan(Span sp) {
  LIBCPP_ASSERT((noexcept(sp.template subspan<Offset, Count>())));
  LIBCPP_ASSERT((noexcept(sp.subspan(Offset, Count))));
  auto s1  = sp.template subspan<Offset, Count>();
  auto s2  = sp.subspan(Offset, Count);
  using S1 = decltype(s1);
  using S2 = decltype(s2);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S1::value_type);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S2::value_type);
  static_assert(S1::extent == Count);
  static_assert(S2::extent == std::dynamic_extent, "");
  return s1.data() == s2.data() && s1.size() == s2.size() && std::equal(s1.begin(), s1.end(), sp.begin() + Offset);
}

template <typename Span, std::size_t Offset>
constexpr bool testConstexprSpan(Span sp) {
  LIBCPP_ASSERT((noexcept(sp.template subspan<Offset>())));
  LIBCPP_ASSERT((noexcept(sp.subspan(Offset))));
  auto s1  = sp.template subspan<Offset>();
  auto s2  = sp.subspan(Offset);
  using S1 = decltype(s1);
  using S2 = decltype(s2);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S1::value_type);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S2::value_type);
  static_assert(S1::extent == (Span::extent == std::dynamic_extent ? std::dynamic_extent : Span::extent - Offset), "");
  static_assert(S2::extent == std::dynamic_extent, "");
  return s1.data() == s2.data() && s1.size() == s2.size() &&
         std::equal(s1.begin(), s1.end(), sp.begin() + Offset, sp.end());
}

template <typename Span, std::size_t Offset, size_t Count>
void testRuntimeSpan(Span sp) {
  LIBCPP_ASSERT((noexcept(sp.template subspan<Offset, Count>())));
  LIBCPP_ASSERT((noexcept(sp.subspan(Offset, Count))));
  auto s1  = sp.template subspan<Offset, Count>();
  auto s2  = sp.subspan(Offset, Count);
  using S1 = decltype(s1);
  using S2 = decltype(s2);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S1::value_type);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S2::value_type);
  static_assert(S1::extent == Count);
  static_assert(S2::extent == std::dynamic_extent, "");
  assert(s1.data() == s2.data());
  assert(s1.size() == s2.size());
  assert(std::equal(s1.begin(), s1.end(), sp.begin() + Offset));
}

template <typename Span, std::size_t Offset>
void testRuntimeSpan(Span sp) {
  LIBCPP_ASSERT((noexcept(sp.template subspan<Offset>())));
  LIBCPP_ASSERT((noexcept(sp.subspan(Offset))));
  auto s1  = sp.template subspan<Offset>();
  auto s2  = sp.subspan(Offset);
  using S1 = decltype(s1);
  using S2 = decltype(s2);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S1::value_type);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S2::value_type);
  static_assert(S1::extent == (Span::extent == std::dynamic_extent ? std::dynamic_extent : Span::extent - Offset), "");
  static_assert(S2::extent == std::dynamic_extent, "");
  assert(s1.data() == s2.data());
  assert(s1.size() == s2.size());
  assert(std::equal(s1.begin(), s1.end(), sp.begin() + Offset, sp.end()));
}

constexpr int carr1[] = {1, 2, 3, 4};
int arr1[]            = {5, 6, 7};

int main(int, char**) {
  {
    using Sp = std::span<const int>;
    static_assert(testConstexprSpan<Sp, 0>(Sp{}), "");

    static_assert(testConstexprSpan<Sp, 0, 4>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 0, 3>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 0, 2>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 0, 1>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 0, 0>(Sp{carr1}), "");

    static_assert(testConstexprSpan<Sp, 1, 3>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 2, 2>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 3, 1>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 4, 0>(Sp{carr1}), "");
  }

  {
    using Sp = std::span<const int, 4>;

    static_assert(testConstexprSpan<Sp, 0, 4>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 0, 3>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 0, 2>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 0, 1>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 0, 0>(Sp{carr1}), "");

    static_assert(testConstexprSpan<Sp, 1, 3>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 2, 2>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 3, 1>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 4, 0>(Sp{carr1}), "");
  }

  {
    using Sp = std::span<const int>;
    static_assert(testConstexprSpan<Sp, 0>(Sp{}), "");

    static_assert(testConstexprSpan<Sp, 0>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 1>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 2>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 3>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 4>(Sp{carr1}), "");
  }

  {
    using Sp = std::span<const int, 4>;

    static_assert(testConstexprSpan<Sp, 0>(Sp{carr1}), "");

    static_assert(testConstexprSpan<Sp, 1>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 2>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 3>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 4>(Sp{carr1}), "");
  }

  {
    using Sp = std::span<int>;
    testRuntimeSpan<Sp, 0>(Sp{});

    testRuntimeSpan<Sp, 0, 3>(Sp{arr1});
    testRuntimeSpan<Sp, 0, 2>(Sp{arr1});
    testRuntimeSpan<Sp, 0, 1>(Sp{arr1});
    testRuntimeSpan<Sp, 0, 0>(Sp{arr1});

    testRuntimeSpan<Sp, 1, 2>(Sp{arr1});
    testRuntimeSpan<Sp, 2, 1>(Sp{arr1});
    testRuntimeSpan<Sp, 3, 0>(Sp{arr1});
  }

  {
    using Sp = std::span<int, 3>;

    testRuntimeSpan<Sp, 0, 3>(Sp{arr1});
    testRuntimeSpan<Sp, 0, 2>(Sp{arr1});
    testRuntimeSpan<Sp, 0, 1>(Sp{arr1});
    testRuntimeSpan<Sp, 0, 0>(Sp{arr1});

    testRuntimeSpan<Sp, 1, 2>(Sp{arr1});
    testRuntimeSpan<Sp, 2, 1>(Sp{arr1});
    testRuntimeSpan<Sp, 3, 0>(Sp{arr1});
  }

  {
    using Sp = std::span<int>;
    testRuntimeSpan<Sp, 0>(Sp{});

    testRuntimeSpan<Sp, 0>(Sp{arr1});
    testRuntimeSpan<Sp, 1>(Sp{arr1});
    testRuntimeSpan<Sp, 2>(Sp{arr1});
    testRuntimeSpan<Sp, 3>(Sp{arr1});
  }

  {
    using Sp = std::span<int, 3>;

    testRuntimeSpan<Sp, 0>(Sp{arr1});
    testRuntimeSpan<Sp, 1>(Sp{arr1});
    testRuntimeSpan<Sp, 2>(Sp{arr1});
    testRuntimeSpan<Sp, 3>(Sp{arr1});
  }

  return 0;
}
